Printing device

ABSTRACT

The invention relates to a printing device for printing sheet elements ( 1 ) that are serially fed to the printing device, in particular product labels made of temperature-sensitive paper or paper substitute materials, comprising a feed device for feeding the sheet elements to a print head which acts on the sheet element, wherein the print head comprises a thermal slat ( 3 ) which is supported flexibly by a carrier device ( 8 ) such that between the thermal slat ( 3 ) and the deflection device ( 4 ) a counterpressure surface is formed at a predefined surface pressure on the sheet element ( 1 ) to be printed. The thermal slat ( 3 ) is associated with an adaptor means ( 7 ) that is exchangeable together with the thermal slat ( 3 ).

The invention relates to a printing device for printing sheet elementsthat are serially fed to the printing device, which sheet elementscomprise a surface material, in particular product labels made oftemperature-sensitive paper or paper substitute materials, comprising afeed device for feeding the sheet elements to a print head which acts onthe sheet element, wherein said print head comprises a thermal slatwhich is supported flexibly by a carrier device such that between thethermal slat and the sheet element a counterpressure surface is formedat a predefined surface pressure on the sheet element to be printed.

Such a printing device is known from DE 100 22 152 A1. This is aprinting device that is designed as a thermal printer in which thethermal slat prints the temperature-sensitive labels by local heating.With this known type of printer, product labels of different widths canbe printed, wherein the width of the thermal slat has to be adapted tothe maximum width of the label to be printed.

From DE 41 39 445 A1 a print head is known which is pretensioned using amultitude of springs that are provided between the print head and endstops of movable shanks.

From DE 33 15 947 A1 a print device is known in which the print head,which comprises the printing plate and a heater for heating the printingplate, is connected to an operating device that is movable in theopposite direction and that comprises elastic elements in the form ofleaf springs.

In printing devices of the type mentioned in the introduction it iscrucial that the surface pressure between the active area of the thermalslat and the label to be printed always remains the same so as to ensuregood print quality. On the other hand the thermal slat, due to itscontact with the surface of labels, is subject to wear and tear whichlimits the service life of the thermal slat. In particular when labelsare printed whose width is considerably less than the width of thethermal slat, the printing device operates in an uneconomical mannerbecause wear and tear in this region leads to failure of the thermalslat although the outer zone of said thermal slat is still functional.Moreover, wider thermal slats are of course more expensive than narrowerones.

Based on the above, it is the object of the invention to improve adevice of the type mentioned in the introduction such that moreeffective use of the thermal slat becomes possible while the printquality remains unchanged.

According to the invention this object is met in that the thermal slatis associated with an adaptor means that is exchangeable together withsaid thermal slat, with which adaptor means the excursion of theresilient holding means for the thermal slat can be adjusted such thatthe surface pressure is constant irrespective of the width of thethermal slat.

The solution according to the invention is characterised in thatdifferent thermal slats, whose widths match the width of the sheetelements to be labelled, can be used easily and without any furtheradjustment measures. An adaptor means is provided which can be exchangedtogether with the thermal slat, which adaptor means is designed suchthat during printing of the sheet element the surface pressure remainsconstant irrespective of the width of the respective thermal slat,without there being a need for adjustment measures.

A preferred embodiment of the solution according to the inventionprovides for adaptation of the surface pressure such that depending onthe width of the thermal slat in use, the thickness of the adaptor meansis varied. This is achieved in that in the case of a wider width of thethermal slat the excursion of the resilient suspension of the thermalslat is greater, while correspondingly in the case of a narrower widthof the thermal slat the excursion is less, so that the surface pressureremains constant irrespective of the width of the thermal slat.

According to a preferred embodiment of the invention this can beachieved with a design that provides for spacers of differentthicknesses to be associated with thermal slats of different widths,wherein such spacers are exchanged together with the thermal slat.

As an alternative, it is also possible to provide a design in whichspacer pins are used, with their length being such that the desiredsurface pressure can be set by way of the excursion of the springsuspension.

A further variant of the invention provides for the thermal slat tocomprise electrical, optical or mechanical identification means thatinteract with the actuators that alter the excursion of the spring suchthat the desired excursion is set according to the width of the thermalslat. This can, for example, be achieved in that electric coding takesplace in the electronics that are associated with the thermal slat,which coding serves as the control value for the actuator. In thisarrangement the position of the excursion is set piezoelectrically,pneumatically, by way of a motor drive or hydraulically.

The solution according to the invention can preferably be applied tosheet elements in the form of product labels. Such product labels caneither be product labels that are removably affixed to a liner strip,which product labels are removable from the liner by means of aso-called peeling-off device, or they can be linerless labels orcontinuous material. Furthermore, it is possible to use thermotransferprint labels in which the print image is transferred from anintermediate medium to the label by heating the thermal slat.

Below, the invention is explained in more detail with reference to adrawing that shows but one embodiment, as follows:

FIG. 1 an embodiment of the invention for use with a thermal slat ofnarrower width; and

FIG. 2 the embodiment of the invention for use with a thermal slat ofwider width.

The printing device shown in FIG. 1 is used for printing sheet elementsin the form of product labels, which sheet elements are fed from a feedunit (not shown) in the form of a take-off reel. The sheet elements inthe form of product labels 1 made of temperature-sensitive paper arefirst fed to a print drum 6 that forms a counterpressure surface, andsubsequently move along the top of a deflection device 4. After thisthey reach the front edge 2 formed at the deflection device 4.

Above the deflection device 4 a stationary carrying element 8 isprovided, on which by way of a sprung holding device 9 an adaptor plate7 is arranged, with a thermal slat 3 being attached to said adaptorplate 7.

The unit comprising the thermal slat 3 and the adaptor plate 7 can belocked or removed using locking means (not shown) in the upper part ofthe printing device shown.

In this arrangement each set comprising the adaptor plate 7 and thethermal slat 3 is designed such that a wide thermal slat 3 is associatedwith an adaptor plate 7 of greater thickness, while a narrower thermalslat is associated with an adaptor plate of lesser thickness. FIG. 1thus shows a first slide-in set comprising a thermal slat of narrowerwidth and an adaptor plate of lesser thickness; and in contrast to this,FIG. 2 shows a wider thermal slat in combination with an adaptor plateof greater thickness.

This matching, according to the invention, of the width of the thermalslat to the thickness of the adaptor plate results in a situation inwhich, in the region of the support surface, the surface pressure actingon the product label 1 to be printed is always the same.

1. A printing device for printing sheet elements (1) that are seriallyfed to the printing device, which sheet elements comprise a surfacematerial, in particular product labels made of temperature-sensitivepaper or paper substitute materials, comprising a feed device forfeeding the sheet elements (1) to a print head which acts on the sheetelement (1), wherein said print head comprises a thermal slat (3) whichis supported flexibly by a carrier device (8) such that between thethermal slat (3) and the sheet element (1) a counterpressure surface isformed at a predefined surface pressure on the sheet element (1) to beprinted, characterised in that the thermal slat (3) is associated withan adaptor means (7) that is exchangeable together with said thermalslat (3), with which adaptor means (7) the excursion of the resilientholding means (9) for the thermal slat (3) can be adjusted such that thesurface pressure is constant irrespective of the width of the thermalslat (3).
 2. The printing device according to claim 1, characterised inthat the adaptor means (7) is an actuator, by way of which the excursionof the holding means (9) is controllable.
 3. The printing deviceaccording to claim 2, characterised in that the actuator is controllablepiezoelectrically, by way of a motor drive, pneumatically, orhydraulically.
 4. The printing device according to claim 1,characterised in that the adaptor means (7) is a spacer affixed to thethermal slat (3), wherein the thickness of said spacer is proportionalto the width of the thermal slat (3).
 5. The printing device accordingto claim 1, characterised in that the adaptor means (7) is a pin elementaffixed to the thermal slat (3), wherein the length of said pin elementis proportional to the width of the thermal slat (3).